Photographic silver halide transfer process



Mam E49 3195@ E. H. LAND PHOTOGRAPHIC SILVER HALIDE TRANSFER PROCESS Filed Nov. 3, 1944 l PHOTSENWV YE? s @P46205 maf/75 grew BY/PMQMW FIG. 5

Patented Mar. 14, 1950 PHUTGRAPEHC SILVER HALDlE TRANSFER PROCESS I f Edwin H. Land, Cambridge, Mass., assigner to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Application November 3, 1944, Serial No'. 561,696

6 Claims.

This invention relates to photography, and more particularly to methods for forming fixed, stable, positive photographic prints.

This application is a continuation-in-part of my copending application Serial No. 539,550, led June 9, 1944, now abandoned, for Photographic product, process and apparatus.

One of the objects of the present invention is to provide a novel process whereby a photographic film, differentially exposed to have formed therein a latent image, is developed and a xed, stable print of said image is obtained.

A still further object is to provide a novel method whereby a novel positive image of the subject matter of a latent image is obtained as a direct product ofthe development of the latent image.

Further objects are the provision of novel photographic processes of the above character whereby the permeaton with a liquid reagent of a photosensitive layer having a latent image formed therein develops the latent image and gives an image-forming component; whereby the image-forming component is translated relative to the material ofthe developed latent image to form in another layer of material a fixed image which is a positive of the subject matter to which the lm was exposed in producing the` latent image; whereby the image-forming component comprises a soluble complex of silver and the desired image is formed by reducing said component to an insoluble product comprising silver in a receiving layer for said component,`

i. e., in a positive print layer; whereby the photosensitive layer acts to dry the receiving layer4 after the formation of the positive image therein; whereby the photosensitive layer tendsto remove from the receiving layer the developer and the complex-forming compound in excess of that which is used to form the positive image in the receiving layer; wherein the positive print layer is a white, nontransparent, water-permeable layer; wherein the positive print layer is a layer of water-permeable, transparent material such as gelatin or regenerated cellulose, preferably mounted on a white, nontransparent and preferably opaque base; and wherein one or more of the substances for the development of the latent image and/or the formation of the fixed positive image is contained in solid form in one of the sheet materials used in the formation of the positive print.

vvThe invention accordingly comprises the several steps and relation and order of one or more of such steps with respect to each of the others, which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims. v

For a fuller understanding of the nature and objects of the invention, reference should be had' to the following detailed description taken in connection with the accompanying drawings wherein: Y

Figure 1 is an enlarged, diagrammatic, fragmentary, sectional view of sheet materials for carrying out one method for forming a fixed positive image in accordance with the present invention;

Fig. 2 is a view similar to Fig. 1 of the fixed positive print obtained by the method and materials illustrated in Fig. 1; l

Fig. 3 is a View similar to Fig. 1 of lm means comprising a photosensitive layer and a receiving layer whereby a modification of the process of the invention may be carried out;

Fig. 4 is an enlarged, diagrammatic, transverse sectional view, with the thicknesses of the materials greatly exaggerated, of a liquid-containing sheet which may be used to provide the liquid reagent for carrying out the novel process of the invention; and

Fig. 5 is a view similar to Fig. 3 of `a modification of the film means of Fig. 3. I

To obtain a positive image in accordance with one method comprehended by the present invention, a photosensitive layer comprising a photosensitive material of the type which is rendered developable by exposure to light, e. g., a silver halide, a mixture of silver halides, or a silver mixed halide, is differentially exposed, for example, in a camera, to predetermined subject matter so as to form therein a latent image of said subject matter. The exposed layer is then permeated with a liquid reagent which com-y prises a developer for reducing the exposed silver salts to silver and a compound for reacting with the undeveloped silver salts to form a silver complex soluble in the reagent. The complexforming reaction takes place at a more rapid rate than the rate at which the developer will reduce the unexposed silver salt whereby a predetermined portion of the unexposed silver salt is transformed to the soluble complex. The positive image of the subject matter to'which the photosensitive layer is exposed is obtained from the soluble silver complex by transporting'said comp-lex to an adjacent receiving layer of waterpermeable material, and reducing said complex in the latter layer to provide an image-forming component comprising silver.

After the formation therein of the image, the

receiving layer may be separated from the photosensitive layer and the image viewed from the side which wasadjacent thephotosensitive layer.

It is also possible to permanently secure the receiving layer to the photosensitive layer and to permeable,v nontransparent opaque, White material suiiciently thin so that the complex silver ions may permeate through said layer to the surface thereof remote from the photosensitive layer to form an image comprising silver visible from the latter surface of said layer.

To remove the liquid reagent from the receiving layer after the formation therein of the positive image, and thereby to dry said receiving layer, it is preferable to select a photosensitive layer which is `substantially thicker than the receiving layer, and to select as the carrier for the photosensitive layer a material which isV more liquidabsorbent than the material of the receiving layer. .For example, the carrier material for the photosensitive layer may be a relatively unhardened gelatin, While the receiving layer may be formed of a substantially more hardened gelatin.

It is also preferable to have the photosensitive layer remove from the receiving layer any developer which remains in said layer after the positive image is formed therein. 'lo eiect this result, the quantity of reagent used for the development of the predetermined area of the photosensitive layer is controlled to provide less developer than is required to develop all of the silver halide in said area. In addition, the reagent is preferably introduced into the photosensitive layer after the exposure of the latter from the side of said layer which is adjacent to the receiving layer. This may be accomplished, for example, by spreading the reagent between the surfaces of the photosensitive and receiving layers as the latter are brought into iace-to-face contact, or by using the receiving layer as the means for transporting the reagent to the photosensitive layer. This concentrates the reagent at the interface of the photosensitive and receiving layers as the image-forming reaction begins. As a result, the developer acts first to develop the exposed silver halide in the portion of the photosensitive layer adjoining the interface and then to develop the silver halide complex which is transported to the receiving layer. After enough time has elapsed to transport the silver complex tothe receiving layer and to orm from said complex the positive silver image, the photosensitive layer is preferablyuniformly exposed to light such as daylight or ordinary room lighting to render the excess silver halide therein developable. As a result, all the remaining developer tends to migrate to the latter layer and to be exhausted therein in the development of the exposed silver halide.

The photosensitive layer may also be employed as the medium for removing any excess of the substance for forming the soluble silver complex with the silver halide. This is accomplished by employing substantially less of said substance than can form a soluble complex With the unexposed silver halide in the photosensitive layer and by selecting as said substance a oompound such as sodium thiosulfate, which, When in the presence of an excess of silver halide, forms an insoluble complex with said halide. The reagent is caused to permeate the photosensitive layer from the side of the latter layer adjoining the receiving layer, and as a result there is an excess of sodium thosulfate at the surface portions of the photosensitive layer. Thus, at the beginning of the reaction, `because of the excess of sodium thiosulfate, there is formed a soluble silver complex which isl transported to the receiving layer, `vvhere it is reduced to silver. However, as the remaining sodium thiosulfate .permeates the photosensitive layer, it encounters an excess of silver halide and forms an insoluble complex with the latter. This tends to concentrate any o the complex-forming substance, in excess of that necessary to form a positive image, in the photosensitive layer.

The photosensive layer is preferably a silver halide emulsion comprising a silver halide, or a mixture of silver halides, or a silver mixed halide in a suitable colloidal carrier, preferably gelatin. Other film-forming colloids may be used as carriers, for example other proteins or their derivatives such as glue and albumen, or Water-permeable organic plastics such as collodion, cellophane, polyhydroxyalkane, polyvinyl alcohol, and certain of the ethers of cellulose. The emulsion may contain any or the various modifying agents ordinarily incorporated in com. mercial emulsione such, for example, as dyes', antihalation layers, overcoatings and sensitizers, and, in fact, suitable materials for provid-ing the photosensitive layers for practicing the invention are the commercially available photographic films and papers. It is to be understood that the llm base may be any material which provides a satisfactory support for the photosensitive layer, although Where the photosensitive layer and the receiving layer are elements of a unitary film structure, it is preferable to mount the photosensitive layer on a base which is transparent so that the latter layer can be exposed through said base.

The image-receiving layer is preferably formed of a Water-permeable material, for example, regenerated cellulose, polyvinyl alcohol, polyhydroxyalkane, sodium alginate, cellulose ethers such as methyl cellulose, or their derivatives such as sodium carboxymethyl cellulose or hydroxyethyl cellulose, papers, proteins" such as glue or gelatin, carbohydrates such as gums and starch, and mixtures of these materials Where the latter are compatible. To form a nontransparent and preferably substantially opaque receiving layer from the'relatively transparent materials, it is possible to incorporate in the latter a suitable pigment, such, for exam-ple, as titanium dioxide, against which an image comprising silver is Visible. Where the receiving layer iste be separated from'the photosensitive layer after the formation of the image therein, it is possible to employ relatively thin, transparent layers of the above materials as the receiving layers and to mount said layers on a nontransparent base, for example, of paper, or a plastico impregnated with a suitable pigment. Where the image is to be formed so as to be visible from the side of the receiving layer remote from the photosensitive layer, a reiatively thin, White, nontransparent, permeable nlm, prei-- erably coated on the remote side with a transparent, permeable film, may be employed as the receiving layer.

If gelatin serves as the receiving layer, it is preferable to at least partially harden the same as by a suitable hardening agent as, for example, potassium alum, potassium chrome alum or formaldehyde.

As 'pointed out above, the novel reagent for permeating the photosensitive layer in accordance with the methods of the invention comprises a substance for developing the exposed silver halide and a substance which reacts with the silver halide to form a silver complex soluble in the reagent, the complex-forming reaction taking place'at a less rapid rate than the development of the exposed silver halide. Substantially all of the known photographic developers may be employed as such in the reagent, provided they do not react with the complex-forming substance.

Examples of preferred developers are hydroquinone, monomethyl-p-aminophenol sulfate, a mixture of hydroquinone and monomethyl-paminophenol sulfate, p-aminophenol hydrochloride, p-hydroxy-phenylaminoacetic acid, p-phenylenediamine, pyrocatechin, and diaminophenolhydrochloride. Other suitable developers are pyrogallol, chlorohydroquinone, o-phenylene diamine, 2oxymethylpaminophenol, and bromohydroquinone. The reagent preferably comprises an aqueous solution of the developer.

Examples of materials which may be used in the yreagent for the purpose of forming a soluble silver complex with the undeveloped silver halide of the photosensitive layer are sodium thiosulfate, ammonium thiosulfate, and ammonia. For obvious reasons, it is preferable that the complexforming substance be one which does not desensitize the silver halide emulsion and one which is not toxic. For example, a compound such as sodium cyanide which will satisfactory photographic results when used in the reagent in accordance with the methods of the invention is generally not desirable because of its toxic character.

The liquid reagent may also contain an accelerator, preferably an alkali such as sodium hydroxide, potassium hydroxide, sodium carbonate, borax, sodium metaborate, paraformaldehyde, or trisodium phosphate, a restrainer such as potassium bromide, potassium iodide, or sodium chloride, and a preservative such as sodium sulte.

In the event that the developer and/or the substance for forming the soluble silver complex is a solid at ambient temperatures, it is Ipossible to incorporate either or both of said substances in solid form in the photosensitive layer and/or the receiving layer. With this arrangement, in order to provide the liquid reagent, the layer or layers containing said solid substances are permeated with a solvent, for example, water, for said substances. This may be accomplished by immersing the layer or layers in a water bath or by bringing into engagement with one of said layers, while the two are juxtaposed, a liquidcontaining sheet,A such as a blotter, saturated with water.

Referring to Fig. l, there are shown diagrammatically materials for carrying out one modication of the method of the present invention, and, as shown, said materials comprise a sheet of` photographic film or paper III which preferably has as its photosensitive layer I2 a silver halidegelatin emulsion, and a positive print member I4which embodies an image-receiving layer I6 preferably mounted on a suitable base I8.

In one Apreferred embodiment of member I4, image-receiving layer I6 is formed of gelatin which is hardened as by immersionin a aqueous solution of formaldehydefor approximately five to fifteen minutes, and base I8 is a cellulosic plastic sheet. To provide a relatively white, opaque background for the silver image, at least the surface layer of the cellulosic base on the side remote from layer `IB is impregnated orcoated with a suitable white pigment 2l) such, for example, as titanium dioxide. Layer I6 is preferably substantially thinner than layer I2.

-.'Ifo practice the invention, iilm I0 is exposed to Apredetermined subject matterA to haveV a latent imageof said subject matter formed inlayer I2. Thereafter, layer I6 of positive print member I4 iimmersed in a solution consisting of;

III)

Sodium sulflte (anhydrous) Water to make cc-- 170 for approximately fifteen seconds. Immediately after the immersion, layer I6 is pressed into face-to-face contact with photosensitive layer I2 in a dark room as, for example, by passing the two sheet materials, i. e., lm IU and positive print member I4, between a pair of squeegee rollers. The films 1are held in contact for approximately one minute in the dark andkthereafter lm IIl, while still in contact with member I4, is exposed uniformly to light for a brief time as, for example, for fifteen seconds in a room illuminated by ordinary incandescent lighting. After the exposure, member I4 is stripped from lm I0 and contains a fixed stable positive of the subject matter of the latent image. The imageforming component 22 (Fig. 2) comprises silver and is the insoluble product of the reaction of the soluble silver complex and the developer, and differs from the silver of conventional photographic images wherein the silver image is obtained by a direct reaction between the exposed silver halide and the developer. It is noted that the imagereceiving layer is brought into face-to-face contact with the photosensitive layer, and as a result the complex which is transported by the reagent from the photosensitive layer to the receiving layer travels such a short distance that no substantial lateral diffusion thereof takes place, a clear and accurate positive being obtained. Although it is preferable to bring the receiving layer into face-to-face contact with the lphotosensitive layer, the process of the invention can be carried out with a layer of relatively permeable material, for example, an antihalation layer, interposed between the 4photosensitive layer and the receiving layer, provided that said intermediate layer is suiiiciently thin so that no substantial lateral diffusion of the soluble complex in its travel from the photosensitive layer to the receiving layer will take place.

In another embodiment of member I4, base I8 I is a cellulose derivative, for example a cellulose ester or mixed ester such as cellulose acetate, cellulose acetate butyrate or cellulose acetate propionate, and layer I6 is formed by regenerating one surface of said derivative to cellulose. A positive print member of this type may be formed by converting to cellulose the surface layer of the nonpigmented side of cellulose acetate, or by converting to cellulose one of the surface layers of a sheet of a mixed cellulose ester impregnated with a white pigment. The conversion may be effected by immersing the side of the sheet in which the cellulose is to be formed in a solution consisting of:

Sodium hydroxide g Methanol cc 10 Water cc After immersion, the sheet is preferably dipped in a 4% solution of sulfuric acid and Washed in water.

It is also possible to use a sheet of regenerated cellulose, i. e., cellophane, as receiving layer I6, and saidsheet may be laminated to a suitable white, nontransparent base such as a sheet oi' a mixed cellulose ester impregnated with a white pigment whereby to provide positive print mem- 7g. ber I4.

Exampiesof othersuitable'positive print members are gelatin coated papers such as imbibition papers, for instance those used` in color photography; gelatin coated plastic or paper films as, for example, bromide papers or process films as for instance moderately slow lms employed for copying purposes, with the silver halide dissolved out and with the gelatin preferably at least par--v tially hardened; relatively pure alpha papers without any coating layer; and the latter papers coated iwith gelatin either in hardened or unhardened condition, the gelatin being cast or rolled thereon. v,

Examples of other novel reagents for forming positive images in accordance with the invention are given below, but it is to be expressly understood that these examples are illustrative only and that the materials as well as the proportions may be varied to a substantial degree, as will now be apparent to those skilled in the art, without departing from the scope of the invention.

Example 1 Sodium suliite (anhydrous) g 9.0 Hydroquinone g 4.5 Sodium hydroxide g 3.75 Potassium bromide g 3.0 Sodium thiosulfate g 5.0 Water to make cc 170 Example 2 Stock solution consisting of:

Water cc 500 Monomethyl p aminophenol sulfate g 3.1 Sodium sulfate (desiccated) g `45.0 Hydroquinone g 12.0 100 cc. S o d i u m carbonate (desiccated) g 67.5 Potassium bromide g-- 1.9 Water to make l 1.0 50% sodium thiosulfate solution cc 3.0 Water cc 100 Example 3 The developing solution of Lumiere and Seyewetz, reported in the British Journal of Photography, January 23, 1925, pages 44 and 45, comprising the following ingredients:

Sodium suliite (anhydrous) g 40 Diamidophenol hydrochloride g 5 Tribasic sodium phosphate g Hypo (crystals) g 25 Water cc 1000 In a modication of the film means of Figs. 1 and 2, nlm l0 and positive print member I4 may be-parts of a composite film. Layer I6 of member .i4 is preferably Vpermeated with the liquid reagent prior tothe assembling of the composite iilm and is separated from the photosensitive layer l2 by a water-vapor impervious liquidretaining sheet. The liquid reagent is retained in layer I' by a suitable water-vapor impervious casing which includes said liquid-retaining sheet. The llatter is constructed so as to be .readily removed from between layers l 2 and I6 so that after exposure of layer i2 said retaining sheet may be removed and layer l5 caused to engage layer l2, permeating the latter layer with the 'liquid reagent and causing the positive image comprising silver to be formed in the former layer. After the formation of the image, the positive print member is separated from lm l0.

{image-receiving layer consists of a sheet jof gel- "atin, cellophane or other relatively Vwater-permeable, transparent, film-forming material withouta backing. The sheet is immersed in the liquid reagent and is then superimposed on-the photosensitive'layer after the exposure of the lat ter. After the positive image isformed in said image-receiving sheet, the latter is separated from the photosensitive layerv and is transferred to a suitable backing sheet, for example of paper or pigmented plastic. If a positive transparency is desired, the meth od of Fig. 1 may be carried out with a'transparent image-receiving layer mounted on 'a transparent base. Y 7 Another form-of lm means whereby the novel method of the present invention may be carried out is shown in-Fig. 3 and comprises a photo-,i sensitive layer 24, supported by a transparent film base'26. Any conventional negative film is satv isfactory for this purpose. There is provided on the surface of photosenstive layer 24 a relatively water-permeable, white and vsubstantially non transparent layer 28 which is vrelatively thin, having a thickness, for example, of the order of .0001 to .0005 inch. l

Layer 23 preferably comprises a water-permeable, lm-forming material as, for example, polyhydroxy alkane, sodium alginate, gelatin, cellulose, methyl cellulose, sodium carboxymethyl cellulose, or polyvinyl alcohol, containing a substantial amount of a relatively white pigment such as titanium dioxide. The nlm-forming material is preferably present only in a suiiicient amount to bind the pigment into a film whereby a maximum pigment content for a predetermined iilm thickness may be obtained. A permeable, relatively opaque layer formed by casting a sheet from a mix-ture of-thirty parts by weight of sodiumalginate and twenty parts by weight of titanium dioxide from a water solution comprising approximately one-hundred seventy-five parts by weight of water and thereafter adhered to the photosensitive layer, for example with Water, gives good results.v

, Examples of other film-forming mixtures which may be used are: gelatin and titanium dioxide, polyhydroxy alkane and titanium dioxide, .hydroxyethyl cellulose 'and titanium dioxide, methyl cellulose arrd titanium dioxide, and sodium `carboxymethyl cellulose and titanium. dioxide. These' mixtures may be cast' from solution directly onto the -photosensitiv'e' layer', or. lmsoi themixtures may be first iormeda'nd then adhered to the photosensitive layer.

Variousv other vmethods for providing these relatively thin, white, nontransparent', permeable films on the photosensitive layer will now be .apparent tofthose skilled in the art, and it is to'b'e expressly understood that films formed by any such methods are within the scope of the present invention; :V In some-instances it may be 'desirable to provide asl an outervsurface for nontransparent'layer 28 a permeable, transparent' iilm, or to have the outer surface portions of said layer 'nonpigmented and transparr'ent.

` To carryout'fthe' novel method of- 'theV inverne tion with this nlm, `photosensitive layer '2 4 is `rst exposed through transparent base 2B and thereafter layers-24 and 28 are permeated by the liquid reagent as by bringing into face-toface contact with layer 28 a sheet 30 which has been immersed in the liquid reagent. The liquid reagent on the surfacel ofvsh'eet 30 is transferred .in the v.liquid reagent.

from Said sheet to layer 28:nd permeates the latter layer -and layer24. The developer' in the reagent reduces the exposed silver halide, and the unexposed silver halide reactswith the complex-forming substance Lto provide `the soluble silver complex. The latter permeates through layer 28 to the outer surface thereof, and when reduced in said layer forms-a Apositive image comprising silver visible fromsaid outer surface.

Layer 28, in addition to'pr'oviding va White background for the positive silver images-acts as'fan'opaque screen to render invisible vthe photo- Sensitive layerand the Ideveloped silver image in the latter layer. `When-thefvpositive Aimage has formed Ain layer, sheet-'30 is separated from the llm.

`Good results are obtained by .using 4a-sheet oil-relatively nonpermeable plasticvsuch as cellulosev acetate as the liquid@transferring sheet 60, provided that said sheet is brought into contact with'layer 28 immediately after the immersion The celluloseacetate, although relatively .nonabsorbent, retains enough reagent on @the surface thereof toefect the desired reaction.

Itis :also kpossible to kprovide the reagent f or 10 exposed, a 4separate roll 'or Apack th'reofflis mounted Within the camera.

An example of a -liquidec'ontaining'sheetmatral of this character is illustrated diagram-"- matieally' `in Fig. 4 as comprising a liquid-con 'taining sheetllnemberiZ such as a blotter ene eased within 'a vapor-impervious lrn, such as a iilrn it of rnetalcoatd,`waxeimpregnated paper'. 1A liquid-retaining Wall I'36 is provided adjacent one surface of liquidecontaining member 321. Wall 3@ may be a relatively brittle plastic, for example styrene, which can be vreadily fractured by the application of mechanical stress, or -it may be a'readily removable lrn of water-Vapor impervious material suchv as a metal-coated, Waximpregnated paper.

rIn a modification of 'the novel method of the invention, the lm means in Fig. 3 is used in conjunction .with a sheetm'aterial (Fig. 5) `com prising a transparent,vbasevillll, for example, Aof cellulose acetate or any other relatively transparent carrier sheet, coated withA a layer 42 formed of a transparent Water-permeable material of the type which may befused as a receive ingy layer. IA preferred `material for this vpurpose is :partially .hardenedtgelatin Aalatent image -i's into -a photosensitive layer comprising a silver halide emulsion containing a latent image Whereby to develop said latent image to silver and to form with unexposed silver halide a silver complex and wherein said complex in solution in said reagent is transferred by imbibition from said photosensitive layer to a permeable imagereceiving layer, held in superposed relation and in relative close proximity to said photosensitive layer, and the silver of said complex is developed by said developer in said image-receiving layer to form therein a reversedimage of said latent image, and wherein said silver halide is in excess of that which is transformed to said complex by said silver halide solvent and wherein said developer is in excess of that required to develop the silver images in both said photosensitive layer and said receiving layer, the improvement which comprises maintaining said photosensitive layer and said image-receiving layer in said superposed relation in the absence of light to which said silver halide is sensitive during the transfer of said complex to said image-receiving layer and the formation therein of said reversed image of said latent image; exposing the photosensitve layer to actinic light without disturbing said superposed relation of said image-receiving layer to fog unexposed silver halide therein and whereby said excess developer is oxidized; and subsequently separating said image-receiving and photosensitive layers from said superposed relation.

2. The process of forming a positive image which comprises developing a latent negative image in a photosensitive layer comprising a silver halide emulsion by substantially uniformly distributing throughout said photosensitive layer while excluding actinic light therefrom an alkaline liquid reagent comprising a photographic developer and a silver halide solvent which forms a soluble and reducible silver complex with unexposed silver halide and providing insaid photosensitive layer developed silver and, in solution in said liquid reagent, a transferable imagewise distribution of silver complex; transferring from said photosensitive layer, by imbibition and while preventing access of actinic light to said photosensitive layer, at least part of said imagewise distribution of said silver complex to an imagereceiving layer superposed with respect to said photosensitive layer in such close proximity as to receive a depthwise diffusion of liquid from said photosensitive layer without appreciably disturbing the imagewise distribution of said dissolved silver complex in said liquid reagent; While still excluding actinic light from said photosensitive layer and without disturbing said close proximity of said emulsion layer to said image-receiv- -ing layer, developing with said developer the silver of said complex in said image-receiving layer whereby to provide a positive image in silver of said latent image, said silver halide being in excess of that which is transformed to said complex by said silver halide solvent and said developer being in excess of that required to develop the silver images in both said photosensitive layer and said receiving layer; substantially uniformly exposing said photosensitive layer to actinic light; retaining said photosensitive layer and said image-receiving layers in said super- -posed relation to permit developer to be accumulated in said photosensitive layer by imbibition Aand to at least partially develop silver halide therein which has been fogged by said uniform exposure whereby said accumulated excess developer is oxidized; and then separating said image-receiving layer from said photosensitive layer.

3. A transfer process as defined in claim 1 wherein the photosensitive layer is characterized as having a greater thickness than said imagereceiving layer whereby to facilitate drying of the image-receiving layer after formation of the reversed image therein and before the imagereceiving layer is separated from said emulsion layer.

4. A transfer process as deined in claim 1 wherein the photosensitive layer is characterized as being formed of a material which is more highly permeable to said liquid reagent than is the material of said image-receiving layer whereby to facilitate drying of the image-receiving layer after formation of the reversed image therein and before the image-receiving layer is separated from said emulsion layer.

5. A transfer process as defined in claim 1 wherein the photosensitive layer is characterized as having a greater thickness than said imagereceiving layer and is formed of a material which is more highly permeable to said liquid reagent than is the material of said image-receiving layer whereby to facilitate drying of the image-receiving layer after formation of the reversed image therein and before the image-receiving layer is separated from the photosensitive layer.

6. A transfer process as defined in claim 1 wherein said photosensitive layer comprises a relatively thick layer of unhardened gelatin and wherein said image-receiving layer comprises a layer of hardened gelatin which is considerably thinner than said photosensitive layer.

EDWIN H. LAND.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,207,042 Hochstetter Dec. 5, 1916 2,013,159 Lierg Sept. 3, 1935 2,196,133 Webb Apr. 2, 1940 2,196,226 Murray et al Apr. 9, 1940 2,216,735 Carothers Oct. 8, 1940 2,273,677 Wallach Feb` 1'7, 1942 2,315,966 Knott Apr. 6, 1943 2,320,108 'ruil May 25, 1943 2,336,902 Tull Dec. 14, 1943 2,350,380 White June 6, 1944 2,352,014 Rott June 20, 1944 2,357,590 Jaffe Sept. 5, 1944 2,361,936 Gaspar Nov. 7, 1944 2,365,345 Kirby et al. Dec. 19, 1944 FOREIGN PATENTS Number Country Date 9,248 Great Britain Apr. 26, 1906 of 1905 382,975 Germany Oct. 9, 1923 714,428 France Dee. 21, 1931 879,995 France Mar. 10, 1943 OTHER REFERENCES Colson, Le Developpement Confine, Bulletin Societe Francaise de Photographie (1898), pages 108 to 111.

Ser. No. 403,392, Rott (A. P. C.) published April 27, 1943.

Certificate of Correction Patent No. 2,500,421 y March 14, 1950 EDWIN H. LAND It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 4, line 53, for plastice read plastic; column 5, line 23, after the Word will insert give; column 11, line 25, for photosensitve read photoseus'itive; column 12, line 66, list of references cited, for 714,428 read 716,428;

and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of August, A. D. 1950.

[will THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents. 

2. THE PROCESS OF FORMING A POSITIVE IMAGE WHICH COMPRISES DEVELOPING A LATENT NEGATIVE IMAGE IN A PHOTOSENSITIVE LAYER COMPRISING A SILVER HALIDE EMULSION BY SUBSTANTIALLY UNIFORMLY DISTRIBUTING THROUGHOUT SAID PHOTOSENSIVE LAYER WHILE EXCLUDING ACTINIC LIGHT THEREFORM AN ALKALINE LIQUID REAGENT COMPRISING A PHOTOGRAPHIC DEVELOPER AND A SILVER HALIDE SOLVENT WHICH FORMS A SOLUBLE AND REDUCIBLE SILVER COMPLEX WITH UNEXPOSED SILVER HALIDE AND PROVIDING IN SAID PHOTOSENSITIVE LAYER DEVELOPED SILVER AND, IN SOLUTION IN SAID LIQUID REAGENT, A TRANSFERABLE IMAGEWISE DISTRIBUTION OF SILVER COMPLEX; TRANSFERRING FROM SAID PHOTOSENSITIVE LAYER, BY IMBITUTION AND WHILE PREVENTING ACCESS OF ACTINIC LIGHT TO SAID PHOTOSENSITIVE LAYER, AT LEAST PART OF SAID IMAGEWISE DISTRIBUTION OF SAID SILVER COMPLEX TO AN IMAGERECEIVING LAYER SUPERPOSED WITH RESPECT TO SAID PHOTOSENSITIVE LAYER IN SUCH CLOSE PROXIMITY AS TO RECEIVE A DEPTHWISE DIFFUSION OF LIQUID FROM SAID PHOTOSENSITIVE LAYER WITHOUT APPRECIABLY DISTURBING THE IMAGEWISE DISTRIBUTION OF SAID DISSOLVED SILVER COMPLEX IN SAID LIQUID REAGENT; WHILE STILL EXCLUDING ACTINIC LIGHT FROM SAID PHOTOSENSITIVE LAYER AND WITHOUT DISTURBING SAID CLOSE PROXIMITY OF SAID EMULSION LAYER TO SAID IMAGE-RECIVING LAYER, DEVELOPING WITH SAID DEVELOPER THE SILVER OF SAID COMPLEX IN SAID IMAGE-RECEIVING LAYER WHEREBY TO PROVIDE A POSITIVE IMAGE IN SILVER OF SAID LATENT IMAGE, SAID SILVER HALIDE BEING IN EXCESS OF THAT WHICH IS TRANSFORMED TO SAID COMPLEX BY SAID SILVER HALIDE SOLVENT AND SAID DEVELOPER BEING IN EXCESS OF THAT REQUIRED TO DEVELOP THE SILVER IMAGES IN BOTH SAID PHOTOSENSITIVE LAYER AND SAID RECEIVING LAYER; SUBSTANTIALLY UNIFORMLY EXPOSING SAID PHOTOSENSITIVE LAYER TO ACTINIC LIGHT; RETAINING SAID PHOTOSENSITIVE LAYER AND SAID IMAGE-RECEIVING LAYERS IN SAID SUPERPOSED RELATION TO PERMIT DEVELOPER TO BE ACCUMULATED IN SAID PHOTOSENSITIVE LAYER BY INHIBITION AND TO AT LEAST PARTIALLY DEVELOP SILVER HALIDE THEREIN WHICH HAS BEEN FOGGED BY SAID UNIFORM EXPOSURE WHEREBY SAID ACCUMULATED EXCESS DEVELOPER IS OXIDIZED; AND THEN SEPARATING SAID IMAGE-RECEIVING LAYER FROM SAID PHOTOSENSITIVE LAYER. 